Highly active and selective catalysts for the production of unsaturated nitriles, methods of making and using the same

ABSTRACT

An improved catalyst for the production of unsaturated nitriles from their corresponding olefins, the catalyst composition having the atomic ratios described by the empirical formula Bi a  Mo b  V c  Sb d  Nb e  Ag f  A g  B h  O x  and methods of using the same.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to new ammoxidation catalysts for theproduction of unsaturated nitriles starting from their correspondingolefins, in particular, for the production of acrylonitrile frompropylene. More specifically, the present invention is directed to animproved ammoxidation catalyst containing niobium and silver asessential elements for enhancing the activity and selectivity of thecatalyst system.

2. Description of Related Art

Several publications are referenced in this application. The referencesdescribe the state of the art to which this invention pertains and arehereby incorporated by reference.

A number of ammoxidation catalysts are known in this field such as thosedisclosed in U.S. Pat. Nos. 4,405,498; 5,688,739; 4,600,541 and EuropeanPatent Publication Nos. 00 32 012 B1; 05 73 713 B1; 04 75 351 A1. All ofthese publications relate to molybdenum catalyst systems.

It is known in the art that the bismuth-molybdenum system plays a roleof electron donor/acceptor mechanisms for selective oxidation andammoxidation. Therefore different mechanisms were proposed based on thisproperty [Delmon et al. (New Development in Selective Oxidation byHeterogeneous Catalysis, Vol. 72, 1992, p. 399-413) and Encyclopedia ofChemical Technology (Kirk-Othmer, Vol. 1, 4th edition, page 358)]. Inthese mechanisms, molybdenum was shown to be responsible for oxygen andnitrogen uptake and insertion into the substrate, while bismuth playsthe role of H-abstraction of the methyl group in the β position.Therefore, bismuth and molybdenum should be present on the catalystsurface in adjacent form in order to form the suitable active phase forthis reaction.

It should be noted that a deficiency of bismuth on the catalyst surfaceleads to total oxidation reactions of the substrate.

It is also well known that antimony plays a role of a donor and thuscould improve the selectivity of a catalytic system. Antimony can alsoplay an additional role by isolating the vanadium active centers whichare highly active towards oxidation reactions. This leads to minimizingthe total oxidation reaction and directs the reaction towards thedesired product.

Many catalysts have been disclosed for the foregoing reactions. One suchcatalyst is described in U.S. Pat. No. 4,062,885, where BiMoSbV systemswere used as active elements. The catalyst was used for the preparationof phthalonitrile by the ammoxidation of ortho-xylene. The use of suchcatalysts for oxidation or ammoxidation reactions involving unsaturatedaliphatic hydrocarbon is not mentioned.

U.S. Pat. No. 4,040,978 relates to a catalyst for a ammoxidationreaction containing bismuth molybdate mixed with other elements.

U.S. Pat. No. 4,405,498 relates to a catalyst for oxidation andammoxidation reactions containing BiMoVSb with additional elements ofgroups IA, IIA, IVA, VA, VIA, IB, IVB and VIIB of the periodic Table ofthe Elements. The patent does not disclose the use of niobium. Although,silver was disclosed, experimental results for the catalyst with silverdid not reflect any performance improvement.

U.S. Pat. No. 4,600,541 relates to a catalyst comprising FeBiMo andpromoters such as Pd, Pt, Os and Ir.

More recently, European Patent Publication No. 0 475 351 A1 relates to acatalyst containing KFeSbMo which could be promoted by Nb and W. Thebest yield was achieved with a catalyst of the formula Fe₁₀ Sb₁₀ Mo₉ Bi₂K₀.6 Ni₅.5 W₀.3 B₀.75 P₀.75 (SiO₂)₇₀.

European Patent Publication No. 0 573 713 B1 relates to a catalystcomprising MoBiFeCoNiCr promoted with at least three other promoters ofalkali metals, alkaline earth metals, rare earth metals, Nb, Tl and As,with Fe, Co, Ni and Cr as essential catalyst components.

U.S. Pat. No. 5,688,739 relates to a multi-component catalyst. The baseof this catalyst is bismuth molybdenum. Germanium was added as anessential element.

None of the prior art references discloses or suggests catalysts whichprovide high performance for the selective production of unsaturatednitriles from their corresponding olefins. Accordingly, it would bedesirable to produce an improved catalyst for use in the selectiveproduction of unsaturated nitrites from their corresponding olefins.

OBJECTS OF THE INVENTION

It is an object of the invention to overcome the above-identifieddeficiencies.

It is another object of the invention to provide a useful catalyst forthe production of nitrites from their corresponding olefins,particularly for the production of acrylonitrile from propylene.

It is a further object of the invention to provide a process for theproduction of acrylonitrile at high yields by vapor phase catalyticammoxidation of propylene in a fluidized or fixed bed reactor.

The foregoing and other objects and advantages of the invention will beset forth in or apparent from the following description.

SUMMARY OF THE INVENTION

The present invention relates to an improved catalyst for the productionof unsaturated nitrites from their corresponding olefins, the catalystincluding a catalytic composition having the atomic ratios described bythe empirical formula set forth below:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e Ag.sub.f A.sub.g B.sub.h O.sub.x,

wherein

A=one or more elements selected from groups VB (e.g., V, Nb, Ta), VIB(e.g., Cr, Mo, W), VIIB (e.g., Mn, Tc Re) or VIII (e.g., Fe, Co, Ni) ofthe periodic table;

B=at least one alkali promoter selected from group IA (e.g, Li, Na, K)or IIA (e.g., Mg, Ca) of the periodic table;

a=0.01 to 12;

b=0.01 to 12;

c=0.01 to 2;

d=0.01 to 10;

e=0.01 to 1;

f=0.0001 to 2, preferably 0.0001 to 1;

g=0 to 2, preferably, 0.01 to 1;

h=0 to 1, preferably, 0.001 to 0.5; and

x=the number of oxygen atoms required to satisfy the valencyrequirements of the elements present.

The numerical values of a, b, c, d, e, f, g, h and x represent therelative gram-atom ratios of the elements, respectively, in the catalystcomposition, where x is a number required to satisfy the valencerequirements of the other elements. The elements are present incombination with oxygen, preferably in the form of various oxides.

The present invention also relates to a process for the catalyticpreparation of unsaturated nitrites from their corresponding olefins,preferably for the production of acrylonitrile or metha acrylonitrile bythe reactions of propylene or isobutylene with molecular oxygen andammonia at temperatures between 200 to 550° C., using the active andselective catalyst of the invention.

Other objects as well as aspects, features and advantages of the presentinvention will become apparent from a study of the presentspecification, including the claims and specific examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the invention relates to an improved ammoxidationcatalytic system for the production of unsaturated nitrites from theircorresponding olefins, in particular, for the production ofacrylonitrile from propylene. More specifically, the present inventionis directed to an improved ammoxidation catalyst containing niobium andsilver as essential elements for enhancing activity and selectivity ofthe catalyst system. The aim of the present invention is to incorporatea new element into the Bi/Mo system which can improve the catalystperformance. This is achieved by incorporating niobium and silver into abismuth/molybdenum/vanadium/antimony catalyst system.

The improved ammoxidation catalytic system of the invention comprisesthe atomic catalyst composition described by the empirical formula setforth below:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e Ag.sub.f A.sub.g B.sub.h O.sub.x,

wherein

A=one or more elements selected from groups VB (e.g., V, Nb, Ta), VIB(e.g., Cr, Mo, W), VIIB (e.g., Mn, Tc Re) or VIII (e.g., Fe, Co, Ni) ofthe periodic table;

B=at least one alkali promoter selected from group IA (e.g, Li, Na, K)or IIA (e.g., Mg, Ca) of the periodic table;

a=0.01 to 12;

b=0.01 to 12;

c=0.01 to 2;

d=0.01 to 10;

e=0.01 to 1;

f=0.0001 to 2, preferably 0.0001 to 1;

g=0 to 2, preferably, 0.01 to 1;

h=0 to 1, preferably, 0.001 to 0.5; and

x=the number of oxygen atoms required to satisfy the valencyrequirements of the elements present.

Accordingly, the aim of this invention is to incorporate silver as a newelement in the Bi/Mo/V/Sb/Nb system which is disclosed in our copendingU.S. application Ser. No. 09,228,885 (Attorney Docket No. KR80576-90),filed concurrently herewith and hereby incorporated by reference, as agood catalyst for the ammoxidation reaction. The silver has the role ofimproving the performance of the catalyst.

The catalysts of the invention can be used with or without a support.Suitable supports for the catalysts include alumina, silica, titania,zirconia, zeolites, silicon carbide, Mo, carbide, molecular sieves andother micro/nonporous materials, and mixtures thereof. When used on asupport, the supported catalyst usually comprises from about 10 to 50%by weight of the catalyst composition, with the remainder being thesupport material.

Another aspect of the invention relates to methods of using the catalystsystem of the invention. More specifically, the invention relates to animproved method of producing unsaturated nitrites from theircorresponding olefins.

One preferred embodiment of the invention relates to an improved processfor the catalytic preparation of acrylonitrile or metha acrylonitrile bythe reaction of propylene or isobutylene with molecular oxygen andammonia at a temperature of between about 200 to 550° C. using theammoxidation catalytic system of the invention.

Preferably, the process achieves a propylene conversion of at least 70%,more preferably at least 75%, even more preferably at least 80%, andmost preferred at least 90% using the catalytic system of the invention.

Preferably, the selectivity in mol % to acrylonitrile is greater than75%, more preferably greater than 80%. The yield of acrylonitrile in mol% is preferably greater than 50%, more preferably greater than 55%, evenmore preferably greater than 60% and most preferred greater than 65%.

EXAMPLES

The following examples are illustrative of some of the products andmethods of making and using the same falling within the scope of thepresent invention. They are, of course, not to be considered in any waylimitative of the invention. Numerous changes and modifications can bemade with respect to the invention.

The basic catalyst of present invention is a mixed metal oxide catalyst,which can be prepared according to any procedure well known by one ofordinary skill the art. Methods used to prepare representative catalystsare given below.

The examples described below are illustrative only and are notconsidered to be in any way limiting to the methods used to make thesecatalysts. The catalysts of the examples were prepared by the methodsdescribed in U.S. Pat. No. 4,405,498.

As used in the following examples, the following terms are defined inthe following manner:

1. "W/F" is defined as the weight of the catalyst in grams divided bythe flow rate of reactant stream in ml/sec measured at S.T.P.

2. "Propylene (C₃ H₆) conversion" is defined as: ##EQU1## 3."Acrylonitrile (ACN) selectivity" is defined as: ##EQU2## 4."Acrylonitrile (ACN) yield" is defined as: ##EQU3##

Example 1

BiMoV₀.175 Sb₀.35 O_(x) /50% Silica

Part A

10.2 g of Sb₂ O₃ was slurried in 20 ml water along with 3.18 g V₂ O₅.The mixture was boiled until it formed a paste. The paste was then driedat 120° C. and calcined under airflow at 760° C. for 2 hrs.

Part B

97 g Bi(NO₃)₃ 5H₂ O was dissolved in 184 ml water and 30 ml HNO₃(concentrated). Separately, 28.78 g MoO₃ was dissolved in 72 ml waterand 30 ml concentrated NH₄ OH. The two solutions were mixed together andthe pH was adjusted to 4 using NH₄ OH. The mixture was then boiled ca. 2hours, filtered and washed with ca. 1000 ml water.

Part C

The pH of 297 g of a silica solution 30% wt % was adjusted with HNO₃ topH=2 to form Part C. Part A and Part B were then added to Part C. Themixture was stirred for several hours, then dried at 120° C. andcalcined under airflow at 550° C.

Example 2

BiMoNb₀.1 V₀.175 Sb₀.35 O_(x) /50% Silica

This catalyst was prepared according to the above described method.Niobium was introduced into the system using the required amount ofniobium penta oxide to the molybdenum solution in Part B. However, anysource of niobium could be used for the same purpose.

Example 3

Ag₀.001 BiMoNb₀.1 V₀.175 Sb₀.35 /50% Silica

The catalyst was prepared according to the method set forth in Example2. Silver was introduced by impregnating 7.147 g of the catalyst ofExample 2 in a solution of 0.0016 g of silver nitrate in 100 cc water.However, any source of silver could be used for the introduction ofsilver into the catalyst by any method. After impregnation, the catalystwas dried and heated to 550° C. for 4 hr under airflow.

Example 4

Ag₀.01 BiMoNb₀.1 V₀.175 Sb₀.35 /50% Silica

The catalyst was prepared according to the method of Example 3, however,0.0158 g of silver nitrate was used for impregnation.

Example 5

BiMoNb₀.1 V₀.9 Sb₀.175 /50% Silica

The catalyst was prepared according to the method of Example 1, however,the nominal amount of vanadium oxide and antimony oxide were reduced byhalf.

Example 6

Ag₀.0001 BiMoNb₀.1 V₀.09 Sb₀.175 /50% Silica

The catalyst was prepared as in Example 5, and impregnated in silvernitrate solution as in Example 3.

Catalyst Test:

The calcined catalysts of the above examples were crushed to 35-60 meshfraction. The crushed catalysts were charged into a tubular fixed bedstainless steel reactor.

The reaction was carried out at 475° C. under atmospheric pressure withthe following feed composition: propylene/O₂ /NH₃ /He=7.9/16.8/10/65.3and a space velocity "W/F"" of 3 or 1.5 as shown in Table No. I.

Comparison:

After reaching the steady state, the reactor effluent was analyzed usinga modern gas chromatograph (HP 6890), equipped with both FID and TCDdetectors. HCN was collected for a given period of time and thentitrated according to the methods described in the literature.

Activity results were calculated according to the equations given above.Results are summarized in Table I.

                                      TABLE I                                     __________________________________________________________________________    Run                 Propylene                                                                           ACN   ACCN                                                                              CO.sub.x                                                                            HCN                                 No.                                                                              CATALYST.sup.1)                                                                             W/F                                                                              Conversion                                                                          Y  S  Y S Y  S  Y  S                                __________________________________________________________________________    1  BiMoV.sub.0.175 Sb.sub.0.35 O.sub.x                                                         3  62.9  48.7                                                                             77.5                                                                             3.1                                                                             4.9                                                                             10.0                                                                             16.0                                                                             0.6                                                                              0.9                              2  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 O.sub.x                                              3  77.4  67.9                                                                             87.7                                                                             2.6                                                                             3.4                                                                             5.3                                                                               6.9                                                                             0.3                                                                              0.3                              3  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 O.sub.x                                              4  81.4  73.1                                                                             89.7                                                                             2.9                                                                             3.5                                                                             5.1                                                                               6.2                                                                             n.m.                                                                             n.m.                             4  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 O.sub.x                                              6  85.4  75.0                                                                             87.8                                                                             4.0                                                                             4.7                                                                             5.9                                                                               6.9                                                                             n.m.                                                                             n.m.                             5  BiMoNb.sub.0.1 V.sub.0.09 Sb.sub.0.175 O.sub.x                                              3  85.6  72.3                                                                             84.5                                                                             1.7                                                                             1.9                                                                             8.2                                                                               9.6                                                                             0.5                                                                              0.6                              6  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 Ag.sub.0.001 O.sub.x                                   1.5                                                                            74.7  62.3                                                                             83.3                                                                             2.4                                                                             3.2                                                                             8.3                                                                              11.2                                                                             1.3                                                                              1.8                              7  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 Ag.sub.0.001 O.sub.x                                 3  90.4  71.6                                                                             79.2                                                                             3.5                                                                             3.9                                                                             12.6                                                                             13.9                                                                             2.3                                                                              2.6                              8  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 Ag.sub.0.01 O.sub.x                                    1.5                                                                            72    58.1                                                                             80.4                                                                             4.4                                                                             6.1                                                                             8.2                                                                              11.3                                                                             1.2                                                                              1.7                              9  BiMoNb.sub.0.1 V.sub.0.175 Sb.sub.0.35 Ag.sub.5.01 O.sub.x                                  3  96.2  77.5                                                                             80.5                                                                             4.5                                                                             4.7                                                                             12.5                                                                             13.0                                                                             1.3                                                                              1.3                              10 BiMoNb.sub.0.1 V.sub.0.09 Sb.sub.0.175 Ag.sub.0.001 O.sub.x                                 3  94.0  77.5                                                                             82.4                                                                             2.6                                                                             2.8                                                                             11.1                                                                             11.8                                                                             1.6                                                                              1.7                              __________________________________________________________________________

Comparing Run Nos. 2 and 7 and Run Nos. 5 and 10 in Table I, it is clearthat the presence of small amount of silver substantially increases theactivity in terms of conversion and acrylonitrile yield. Comparisonbetween Run Nos. 7 and 9 shows that, the addition of slightly moresilver further improves catalyst performance.

This clearly demonstrates that the presence of silver is essential insubstantially enhancing the catalyst performance as claimed in thepresent invention.

The addition of silver to the BiMoNbVSb catalyst also promotes theCO_(x) and HCN formation. However, the overall yield of acrylonitrilewas in general improved. Therefore, it can be concluded that silverenhances the activity of this catalyst system for acrylonitrileproduction.

The above description of the invention is intended to illustrative andnot limiting. Various changes or modifications in the embodimentsdescribed may occur to those skilled in the art. These can be madewithout departing from the spirit or scope of the invention.

We claim:
 1. A catalyst system for the production of unsaturatednitrites from the corresponding olefins comprising a catalystcomposition having the empirical formula:

    Bi.sub.a Mo.sub.b V.sub.c Sb.sub.d Nb.sub.e Ag.sub.f A.sub.g B.sub.h O.sub.x,

wherein A is one or more elements selected groups VB, VIB, VIIB or VIIIof the periodic table; B is at least one alkali or alkaline earth metalpromoter selected from groups IA or IIA of the periodic table; a=0.01 to12; b=0.01 to 12; c=0.01 to 2; d=0.01 to 10; e=0.01 to 1; f=0.0001 to 2;g=0 to 2; h=0 to 1; and x=the number of oxygen atoms required to satisfythe valency requirements of the elements present.
 2. The catalyst systemof claim 1, wherein f is from 0.0001 to
 1. 3. The catalyst system ofclaim 1, wherein said olefins are selected from propylene, isobutyleneor mixtures thereof and said nitrites are selected from acrylonitrile,methacrylonitrile or mixtures thereof.
 4. The catalyst system of claim1, wherein said catalyst composition is supported on a catalyst supportmaterial selected from silica, alumina, zirconia, titania, alundum,silicon carbide, alumina-silica, inorganic phosphates, silicates,aluminates, borates and carbonates, pumice, montmorillonite, or mixturesthereof, thereby providing said catalyst system.
 5. The catalyst systemof claim 4, wherein said catalyst support material is silica.
 6. Thecatalyst system of claim 1, wherein the catalyst system furthercomprises a support material and said catalyst system comprises fromabout 10-50% by weight catalyst composition with the remainder being thesupport material.
 7. The catalyst system of claim 1, wherein g rangesfrom 0.01 to 1 and h ranges from 0.001 to 0.5.